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Journal Articles

New antiferromagnetic order with pressure-induced superconductivity in EuFe$$_2$$As$$_2$$

Ikeda, Shugo*; Tsuchiya, Yu*; Zhang, X.-W.*; Kishimoto, Shunji*; Kikegawa, Takumi*; Yoda, Yoshitaka*; Nakamura, Hiroki; Machida, Masahiko; Glasbrenner, J.*; Kobayashi, Hisao*

Physical Review B, 98(10), p.100502_1 - 100502_6, 2018/09

 Percentile:100(Materials Science, Multidisciplinary)

The interplay between magnetism and superconductivity is one of important subjects to investigate the pairing mechanism in novel superconductors. We have found new coexistence between an antiferromagnetic order in the Fe sublattice and superconductivity of the FeAs-based EuFe$$_2$$As$$_2$$ superconductor in the pressure range from 2.4 to 3.0 GPa by $$^{57}$$Fe nuclear forward scattering (NFS) using a single crystal sample. The magnetic state in the Fe sublattice changes to a new antiferromagnetic one with superconductivity from a stripe-type antiferromagnetic one observed in normal conducting state at 2.7 GPa. Below the superconducting transition temperature, the temperature dependence of $$^{57}$$Fe NFS spectra reveals that the new antiferromagnetic order develops with the superconductivity. This non-trivial coupling of two ordered states in EuFe$$_2$$As$$_2$$ under pressure demonstrates a new and intriguing relationship between magnetism and superconductivity in Fe-based superconductors.

Journal Articles

Spin state of Co$$^{3+} $$ in LaCo$$_{1-x}$$ Rh$$_{x}$$O$$_{3}$$ investigated by structural phenomena

Asai, Shinichiro*; Okazaki, Ryuji*; Terasaki, Ichiro*; Yasui, Yukio*; Kobayashi, Wataru*; Nakao, Akiko*; Kobayashi, Kensuke*; Kumai, Reiji*; Nakao, Hironori*; Murakami, Yoichi*; et al.

Journal of the Physical Society of Japan, 82(11), p.114606_1 - 114606_6, 2013/11

 Times Cited Count:6 Percentile:46.59(Physics, Multidisciplinary)

Neutron and synchrotron X-ray diffraction for LaCo$$_{1-x}$$ Rh$$_{x}$$O$$_{3}$$ have been carried out in order to investigate the structural properties related with the spin state of Co$$^{3+}$$ ions. We have found that the values of the Co(Rh)-O bond lengths in the Co(Rh)O$$_{6}$$ octahedron of LaCo$$_{0.8}$$Rh$$_{0.2}$$O$$_{3}$$ are nearly identical at 10 K. The lattice volume for the Rh$$^{3+}$$ substituted samples decreases with the thermal expansion coefficient similar to that of LaCoO$$_{3}$$ from room temperature, and ceases to decrease around 70 K. These experimental results favor a mixed state consisting of the high-spin state and low-spin state Co$$^{3+}$$ ions, and suggest that the high-spin state Co$$^{3+}$$ ions are thermally excited in addition to those pinned by the substituted Rh$$^{3+}$$ ions.

JAEA Reports

Construction of a car-borne survey system for measurement of dose rates in air; KURAMA-II, and its application

Tsuda, Shuichi; Yoshida, Tadayoshi; Nakahara, Yukio; Sato, Tetsuro; Seki, Akiyuki; Matsuda, Norihiro; Ando, Masaki; Takemiya, Hiroshi; Tanigaki, Minoru*; Takamiya, Koichi*; et al.

JAEA-Technology 2013-037, 54 Pages, 2013/10


JAEA has been performing dose rate mapping in air using a car-borne survey system KURAMA-II. The KURAMA system is a GPS-aided mobile radiation monitoring system that has been newly developed by Kyoto University Research Reactor Institute in response to the nuclear disaster. The KURAMA system is composed of an energy-compensated scintillation survey meter for measuring dose rate, electric device for controlling both the dose rates and the position data from a GPS module, a computer server for processing and analyzing data from KURAMA, and client PCs for providing for end users. The KURAMA-II has been improved in small-packaging, durability, and automated data transmission. In consequence, dose rate mapping in wide area has become possible in shorter period of time. This report describes the construction of KURAMA-II, its application and a suggestion of how to manage a large number of KURAMA-II.

Journal Articles

Improved sensitivity of magnetic measurements under high pressure in miniature ceramic anvil cell for a commercial SQUID magnetometer

Tateiwa, Naoyuki; Haga, Yoshinori; Matsuda, Tatsuma*; Fisk, Z.; Ikeda, Shugo*; Kobayashi, Hisao*

Review of Scientific Instruments, 84(4), p.046105_1 - 046105_3, 2013/04

 Times Cited Count:11 Percentile:35.57(Instruments & Instrumentation)

Two modifications have been made to a miniature ceramic anvil high pressure cell (mCAC) designed for magnetic measurements in a commercial superconducting quantum interference (SQUID) magnetometer. Replacing the Cu-Be piston in the former mCAC with a composite piston composed of the Cu-Be and ceramic cylinders reduces the background magnetization significantly smaller at low temperatures. A second modification to the mCAC is the utilization of a ceramic anvil with a hollow in the center of the culet surface.

Journal Articles

Observation of a pressure-induced As-As hybridization associated with a change in the electronic state of Fe in the tetragonal phase of EuFe$$_2$$As$$_2$$

Kobayashi, Hisao*; Ikeda, Shugo*; Sakaguchi, Yui*; Yoda, Yoshitaka*; Nakamura, Hiroki; Machida, Masahiko

Journal of Physics; Condensed Matter, 25(2), p.022201_1 - 022201_6, 2013/01

 Times Cited Count:7 Percentile:54.93(Physics, Condensed Matter)

The electronic and vibrational properties of EuFe$$_2$$As$$_2$$ in the tetragonal phase between 0 and 5 GPa have been investigated using $$^{57}$$Fe M$"o$ssbauer spectroscopy and $$^{57}$$Fe nuclear resonance inelastic scattering, respectively. We find a discontinuous increase of the center shift around 2.3 GPa, reflecting a change of the electronic state of Fe, and above 2.5 GPa a softening of the optical phonon modes associated with an increase of the relative volume of the FeAs$$_4$$ tetrahedron in the unit cell. Our findings reveal that an effective As-As hybridization along the c axis appears at approximately 2.3 GPa in the tetragonal phase of EuFe$$_2$$As$$_2$$, along with a change in the electronic state of Fe, causing bulk superconductivity to appear at a low temperature. Consequently, the change in the electronic state of the Fe atom and the effective As-As hybridization play key roles in the pressure-induced superconductivity in the tetragonal phase of AFe$$_2$$As$$_2$$.

Journal Articles

Study on the oxygen adsorption property of nitrogen-containing metal-free carbon-based cathode catalysts for oxygen reduction reaction

Kiuchi, Hisao*; Niwa, Hideharu*; Kobayashi, Masaki*; Harada, Yoshihisa*; Oshima, Masaharu*; Chokai, Masayuki*; Nabae, Yuta*; Kuroki, Shigeki*; Kakimoto, Masaaki*; Ikeda, Takashi; et al.

Electrochimica Acta, 82(1), p.291 - 295, 2012/10

 Times Cited Count:10 Percentile:63.21(Electrochemistry)

We study the characteristics of oxygen adsorption on metal-free carbon-based cathode catalysts derived from nitrogen-containing polyamide (PA) and nitrogen-free phenolic resin (PhRs). Electrochemical analysis and Raman spectroscopy showed higher 2-electron oxygen reduction reaction (ORR) activity and more defect sites in PA than PhRs. The increase in the amount of adsorbed oxygen in PA was also identified by oxygen adsorption isotherms. ${it In-situ}$ X-ray photoelectron spectroscopy reveals that graphite-like nitrogen contributes to oxygen adsorption and C=O components are dominant in PA. These experimental results indicate that the adsorbed C=O components near the graphite-like nitrogen can be assigned as active sites for 2-electron ORR.

Journal Articles

Orthorhombic fluctuations in tetragonal $$A$$Fe$$_2$$2As$$_2$$ ($$A$$ = Sr and Eu)

Kobayashi, Hisao*; Ikeda, Shugo*; Yoda, Yoshitaka*; Nakamura, Hiroki; Machida, Masahiko

Physical Review B, 84(18), p.184304_1 - 184304_7, 2011/11

 Times Cited Count:7 Percentile:59.49(Materials Science, Multidisciplinary)

The structural and magnetic phase transition in $$A$$Fe$$_2$$As$$_2$$ ($$A$$ = Sr and Eu) was investigated from the viewpoint of the Fe-specific phonon density of states, $$g$$$$^{e}$$$$_{rm Fe}$$($$E$$), utilizing $$^{57}$$Fe nuclear resonant inelastic-scattering and ab initio phonon calculations. The Fe optical phonon branches in $$g$$$$^{e}$$$$_{rm Fe}$$($$E$$) around 25 meV show no anomalies across the phase transition temperature, $$T_{rm SDW}$$, with decreasing temperature. Meanwhile, the peak intensity around 32 meV decreases and increases at 1.25$$T_{rm SDW}$$ and $$T_{rm SDW}$$, respectively, which originates from phonon branches involving Fe and As atomic displacements in the tetragonal structure. This decrease is related to the phonon branches involving atomic displacements in the ab plane. Furthermore, the average sound velocity below 8 meV shows no temperature dependence down to $$T_{rm SDW}$$, suggesting softening in some of the sound waves. Our results indicate the presence of orthorhombic fluctuations in tetragonal $$A$$Fe$$_2$$As$$_2$$.

Journal Articles

Design and characteristics of the JRR-3M thermal neutron radiography facility and its imaging systems

Matsubayashi, Masahito; Kobayashi, Hisao*; Hibiki, Takashi*; Mishima, Kaichiro*

Nuclear Technology, 132(2), p.309 - 324, 2000/11

 Times Cited Count:24 Percentile:15.53(Nuclear Science & Technology)

no abstracts in English

Journal Articles

Neutron and $$gamma$$ ray radiography using a multi-color converter

Iwata, Hideki*; Mochiki, Koichi*; Murata, Yutaka*; Nitto, Koichi*; Tamura, Toshiyuki*; Kobayashi, Hisao*; Matsubayashi, Masahito

Dai-3-Kai Hoshasen Ni Yoru Hihakai Hyoka Shimpojiumu Koen Rombunshu, p.142 - 147, 1999/11

no abstracts in English

Oral presentation

Phonon measurement in SrFe$$_2$$As$$_2$$

Fukuda, Tatsuo; Kobayashi, Hisao*; Ikeda, Shugo*; Tsuchiya, Yu*; Tsutsui, Satoshi*; Baron, A. Q. R.*; Nakamura, Hiroki; Machida, Masahiko

no journal, , 

no abstracts in English

Oral presentation

Diverse magnetic anisotropy in divalent Eu intermetallic family Eu$$T$$In$$_4$$

Kaneko, Koji; Ikeda, Shugo*; Frontzek, M. D.*; Cao, H.*; Hanashima, Takayasu*; Nakao, Akiko*; Kiyanagi, Ryoji; Ohara, Takashi; Kobayashi, Hisao*; Yamagami, Hiroshi

no journal, , 

no abstracts in English

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